388 research outputs found
Binary pattern codification strategies in an active stereoscopic system based on flexible image guides
International audienceA wide variety of three dimensional (3D) measurement systems that can extract shape information's with sub millimetric accuracy is available in the industry. However, they generally are of macroscopic size and measuring on confined areas is not feasible. To miniaturize such systems, the step proposed is the integration of flexible image guides combined with compact optical probes. This miniaturization process is tested on an active stereoscopic measurement system. In the projection channel of the system, a digital micro-mirror device (DMD) generates structured binary patterns from an incoherent white light source and injects them into a first image guide. Then, a compact optical system projects the pattern on the measurement area. The same configuration principle is applied to the acquisition channel and allows the capture of the measurement area through a second image guide and finally to a digital camera. In this miniaturized system, image guides have lower resolution than in standard imaging devices. Indeed they are equivalent of 70k pixels devices to compare to the almost 800k pixels of the DMD and camera. That implies lower axial and lateral resolutions and consequently the shape reconstruction method must be carefully chosen. In this paper, several reconstruction strategies such as tuning the projected patterns frequency and also phase-shfit versus gray code based methods were compared considering the best axial resolution criteria
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GNSS Signal Authentication via Power and Distortion Monitoring
We propose a simple low-cost technique that enables
civil Global Positioning System (GPS) receivers and other civil
global navigation satellite system (GNSS) receivers to reliably
detect carry-off spoofing and jamming. The technique, which
we call the Power-Distortion detector, classifies received signals
as interference-free, multipath-afflicted, spoofed, or jammed
according to observations of received power and correlatio
n
function distortion. It does not depend on external hardware or
a network connection and can be readily implemented on many
receivers via a firmware update. Crucially, the detector can with
high probability distinguish low-power spoofing from ordinary
multipath. In testing against over 25 high-quality empirical data
sets yielding over 900,000 separate detection tests, the detector
correctly alarms on all malicious spoofing or jamming attack
s
while maintaining a
<0.5% single-channel false alarm rate.Aerospace Engineering and Engineering Mechanic
Oblate Schwarzschild approximation for polarized radiation from rapidly rotating neutron stars
We have developed a complete theory for the calculation of the observed
Stokes parameters for radiation emitted from the surface of a rapidly rotating
neutron star (NS) using the oblate Schwarzschild approximation. We accounted
for the rotation of the polarization plane due to relativistic effects along
the path from the stellar surface to the observer. The results were shown to
agree with those obtained by performing full numerical general relativistic
ray-tracing with the \textsc{arcmancer} code. We showed that the obtained
polarization angle (PA) profiles may differ substantially from those derived
for a spherical star. We demonstrated that assuming incorrect shape for the
star can lead to biased constraints for NS parameters when fitting the
polarization data. Using a simplified model, we also made a rough estimate of
how accurately the geometrical parameters of an accreting NS can be determined
using the X-ray polarization measurements of upcoming polarimeters like the
Imaging X-ray Polarimeter Explorer (IXPE) or the enhanced X-ray Timing and
Polarimetry (eXTP) mission.Comment: 11 pages, 10 figures, accepted in A&
ON THE STRUCTURE AND INVARIANTS OF CUBICAL COMPLEXES
This dissertation introduces two new results for cubical complexes. The first is a simple statistic on noncrossing partitions that expresses each coordinate of the toric h-vector of a cubical complex, written in the basis of the Adin h-vector entries, as the total weight of all noncrossing partitions. This expression can then be used to obtain a simple combinatorial interpretation of the contribution of a cubical shelling component to the toric h-vector.
Secondly, a class of indecomposable permutations, bijectively equivalent to stan- dard double occurrence words, may be used to encode one representative from each equivalence class of the shellings of the boundary of the hypercube. Finally, an adja- cent transposition Gray code is constructed for this class of permutations, which can be implemented in constant amortized time
Evaluating the role of the State and non-State actors in mitigating water shortages in Ethekwini municipality.
Masters Degree. University of KwaZulu- Natal, Durban.Water is one of the necessities needed for survival but due to the changing climate it has become scarce in many parts of the world, including South Africa. An investigation into the role of the state and non-state actors within the Department of Water and Sanitation in the eThekwini municipality serves as a departure point from which to critically examine the inclusion of the Millennium Development Goals within strategies and policies put in place by the eThekwini Municipality to promote water conservation and to ascertain how the state and non-state actors contribute in mitigating water shortages within the eThekwini Municipality. The collective problems of water scarcity are evident and will grow over time. This study used an environmental lens into understanding and examining the phenomenon of water scarcity and considered the link between governance as applied to water and how water is an important resource in reducing poverty and playing a part towards economic development of the country. This was highlighted in order to reveal the missing mechanisms of governance that would help public organizations and other stakeholders to take on joint responsibility for the water scarcity issue, because it is a long-term problem.
This study employed a qualitative research design. Eleven semi-structured interviews with Department of Water and Sanitation representatives and the water management forum representative from the eThekwini Municipality were conducted. These were face-to-face interviews which were subsequently transcribed, and key themes were then developed, analysed and interpreted. Secondary data that were employed in this study was extracted from relevant journal articles, academic database websites and books. The transcribed interviews were thematically analysed. The findings revealed the ways in which the current water crisis can be used to find new solutions or practical ways such as the shift towards more water-efficient waste-management technologies. Furthermore, an evaluation of the role of the state in water mitigation measures is provided, based on the results of the qualitative data analysis. South Africa is a water stressed country with rising pressure on its water resources. The study recommends urgent solutions to protect water resources within this rapidly-developing country
Paving the way for transitions --- a case for Weyl geometry
This paper presents three aspects by which the Weyl geometric generalization
of Riemannian geometry, and of Einstein gravity, sheds light on actual
questions of physics and its philosophical reflection. After introducing the
theory's principles, it explains how Weyl geometric gravity relates to
Jordan-Brans-Dicke theory. We then discuss the link between gravity and the
electroweak sector of elementary particle physics, as it looks from the Weyl
geometric perspective. Weyl's hypothesis of a preferred scale gauge, setting
Weyl scalar curvature to a constant, gets new support from the interplay of the
gravitational scalar field and the electroweak one (the Higgs field). This has
surprising consequences for cosmological models. In particular it leads to a
static (Weyl geometric) spacetime with "inbuilt" cosmological redshift. This
may be used for putting central features of the present cosmological model into
a wider perspective.Comment: 54 pp, 2 figs. To appear in D. Lehmkuhl (ed.) "Towards a Theory of
Spacetime Theories", Einstein Studies, Basel: Birkhaeuser), revised version
June 201
Performance evaluation of coherent WDM PS-QPSK (HEXA) accounting for non-linear fiber propagation effects
Coherent-detection (CoD) permits to fully exploit the fourdimensional
(4D) signal space consisting of the in-phase and quadrature
components of the two fiber polarizations. A well-known and successful
format exploiting such 4D space is Polarization-multiplexed QPSK
(PM-QPSK). Recently, new signal constellations specifically designed and
optimized in 4D space have been proposed, among which polarizationswitched
QPSK (PS-QPSK), consisting of a 8-point constellation at the
vertices of a 4D polychoron called hexadecachoron. We call it HEXA
because of its geometrical features and to avoid acronym mix-up with
PM-QPSK, as well as with other similar acronyms. In this paper we
investigate the performance of HEXA in direct comparison with PM-QPSK,
addressing non-linear propagation over realistic links made up of 20 spans
of either standard single mode fiber (SSMF) or non-zero dispersion-shifted
fiber (NZDSF). We show that HEXA not only confirms its theoretical
sensitivity advantage over PM-QPSK in back-to-back, but also shows a
greater resilience to non-linear effects, allowing for substantially increased
span loss margins. As a consequence, HEXA appears as an interesting
option for dual-format transceivers capable to switch on-the-fly between
PM-QPSK and HEXA when channel propagation degrades. It also appears
as a possible direct competitor of PM-QPSK, especially over NZDSF fiber
and uncompensated links
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